Shaped polyethylene articles of intermediate molecular weight and high modulus

ABSTRACT

Solutions of intermediate molecular weight polymers from about 200,000 to about 4,000,000, such as polyethylene, in a relatively non-volatile solvent are extruded through an aperature at constant concentration and thereafter stretched at a ratio of at least about 3:1 prior to cooling to form a first gel. The first gels are extracted with a volatile solvent to form a second gel, and the second gel is dried to form a low porosity xerogel. Stretching occurs with any one or more of the first gel, second gel or xerogel. The polyethylene products produced by our process include products having a molecular weight between about 200,000 and about 4,000,000 a tenacity of at least about 13 grams/denier, a modulus of at least about 350 gram/denier, a porosity of less than 10% by volume, a crystalline orientation function of at least about 0.95, and a main melting temperature of at least about 140° C.

This application is a continuation of application Ser. No. 08/107,421filed Aug. 16, 1993, now abandoned which is a continuation of Ser. No.07/629,183 filed on Dec. 21, 1990 (abandoned), which is a continuationof Ser. No. 07/241,800 filed on Sep. 6, 1988 (abandoned), which is acontinuation of Ser. No. 06/812,709 filed on Dec. 23, 1985 (abandoned),which is a divisional of Ser. No. 06/690,914 filed on Jan. 11, 1985,(U.S. Pat. No. 4,663,101).

BACKGROUND OF THE INVENTION

The present invention relates to intermediate molecular weight shapedpolyethylene articles such as polyethylene fibers exhibiting relativelyhigh tenacity, modulus and toughness, and to products made therefrom.The polyethylene article is made by a process which includes the step ofstretching a solution of polyethylene dissolved in a solvent at astretch ratio of at least about 3:1.

Polyethylene fibers, films and tapes are old in the art. An early patenton this subject appeared in 1937 (G.B. 472,051). However, untilrecently, the tensile properties of such products have been generallyunremarkable as compared to competitive materials, such as thepolyamides and polyethylene terephthalate. Recently, several methodshave been discovered for preparing continuous low and intermediatemolecular weight polyethylene fibers of moderate tensile properties.Processes for the production of relatively low molecular weight fibers(a maximum weight average molecular weight, Mw, of about 200,000 orless) have been described in U.S. Pat. Nos. 4,276,348 and 4,228,118 toWu and Black, U.S. Pat. Nos. 3,962,205, 4,254,072, 4,287,149 and4,415,522 to Ward and Cappaccio, and U.S. Pat. No. 3,048,465 toJurgeleit. U.S. Pat. No. 4,268,470 to Cappaccio and Ward describes aprocess for producing intermediate molecular weight polyolefin fibers(minimum molecular weight of about 300,000).

The preparation of high strength, high modulus polyolefin fibers bysolution spinning has been described in numerous recent publications andpatents. German Off. No. 3,004,699 to Smith et al. (Aug. 21, 1980)describes a process in which polyethylene is first dissolved in avolatile solvent, the solution is spun and cooled to form a gelfilament, and, finally, the gel filament is simultaneously stretched anddried to form the desired fiber. U.K. Patent Application No. 2,051,667to P. Smith and P. J. Lemstra (Jan. 21, 1981) discloses a process inwhich a solution of a polymer is spun and the filaments are drawn at astretch ratio which is related to the polymer molecular weight, at adrawing temperature such that at the draw ratio used, the modulus of thefilaments is at least 20 GPa (the application notes that to obtain thehigh modulus values required, drawing must be performed below themelting point of the polyethylene; in general, at most 135° C.). Kalband Pennings in Polymer Bulletin, Volume 1, pp. 879-80 (1979), J. Mat.Sci., Vol. 15, pp. 2584-90 (1980) and Smook et al. in Polymer Mol., Vol2, pp. 775-83 (1980).describe a process in which the polyethylene isdissolved in a non-volatile solvent (paraffin oil), the solution iscooled to room temperature to form a gel which is cut into pieces, fedto an extruder and spun into a gel filament, the gel filament beingextracted with hexane to remove the parafin oil, vacuum dried andstretched to form the desired fiber.

Most recently, ultra high molecular weight fibers have been disclosed.U.S. Pat. No. 4,413,110 to Kavesh and Prevorsek describes a solutionspun fiber of from 500,000 molecular weight to about 8,000,000 molecularweight which exhibits exceptional modulus and tenacity. U.S. Pat. Nos.4,430,383 and 4,422,993 to Smith and Lemstra also describe a solutionspun and drawn fibers having a minimum molecular weight of about800,000. U.S. Pat. No. 4,436,689 to Smith, Lemstra, Kirschbaum andPijers describes solution spun filaments of molecular weight greaterthan 400,000 (and an Mw/Mn<5). In addition, U.S. Pat. No. 4,268,470 toWard and Cappacio also discloses high molecular weight polyolefinfibers.

In general, the known processes for forming polyethylene and otherpolyolefin fibers may be observed as belonging in one of two groups:those which describe fibers of low average molecular weight (200,000 orless) and those which describe fibers of high average molecular weight(800,000 or more). Between the two groups, there is a molecular weightrange which has not been accessible to the prior art methods forpreparing fibers of high tensile properties.

There are advantages to the molecular weight ranges thus far mastered.Lower molecular weight polymers are generally synthesized and processedinto fibers more easily and economically than high molecular weightfibers. On the other hand, fibers spun from high molecular weightpolymers may possess high tensile properties, low creep, and highmelting point. A need exists for fibers and methods which bridge thisgap, combining good economy with moderate to high tensile properties.Surprisingly, our process makes it possible to accomplish these results.

BRIEF DESCRIPTION OF THE INVENTION

The present invention is directed to novel shaped polyethylene articleshaving a weight average molecular weight between about 200,000 and about4,000,000, a crystalline orientation function of at least about 0.95, atensile modulus of at least about 350 grams/denier, a tenacity of atleast about 13 grams/denier, and a main melting temperature of at leastabout 140° C. (measured at 10° C./minute heating rate by differentialscanning calorimetry), said main melting temperature being greater thanthe main melting temperature of a shaped polyethylene article ofsubstantially the same weight average molecular weight produced from apolymer solution of substantially the same polymer concentration, spunat substantially the same throughput rate and subjected to solutionstretching at a ratio of less than about 3:1.

The present invention is directed to novel shaped polyethylene articleshaving a weight average molecular weight between about 200,000 and about800,000, a crystalline orientation function of at least about 0.95, atensile modulus of at least about 350 grams/denier, a tenacity of atleast about 13 grams/denier, and a main melting temperature of at leastabout 140° C. (measured at 10° C./minute heating rate by differentialscanning calorimetry), said main melting temperature being greater thanthe main melting temperature of a shaped polyethylene article ofsubstantially the same weight average molecular weight produced from apolymer solution of substantially the same polymer concentration, spunat substantially the same throughput rate and subjected to solutionstretching at a ratio of less than about 3:1.

The present invention is also drawn to novel shaped polyethylenearticles having a weight average molecular weight between about 250,000and 750,000, a crystalline orientation function of at least about 0.95,a tensile modulus of at least about 500 grams/denier, a tenacity of atleast about 15 grams/denier, and a main melting temperature of at leastabout 141° C. (measured at 10° C./minute heating rate by differentialscanning calorimetry), said main melting temperature being greater thanthe main melting temperature of a shaped polyethylene article ofsubstantially the same weight average molecular weight produced from apolymer solution of substantially the same polymer concentration, spunat substantially the same throughput rate and subjected to solutionstretching at a ratio of less than about 3:1.

The present invention also includes novel shaped polyethylene articlesof substantially indefinite length having a weight average molecularweight between about 250,000 and 750,000, a crystalline orientationfunction of at least about 0.95, a tensile modulus of at least about 750grams/denier, a tenacity of at least about 18 grams/denier, and a mainmelting temperature of at least about 141° C. (measured at 10° C./minuteheating rate by differential scanning calorimetry), said main meltingtemperature being greater than the main melting temperature of a shapedpolyethylene article of substantially the same weight average molecularweight produced from a polymer solution of substantially the samepolymer concentration, spun at substantially the same throughput rateand subjected to solution stretching at a ratio of less than about 3:1.

The present invention also includes novel shaped polyethylene articlesof substantially indefinite length having a weight average molecularweight between about 300,000 and 700,000, a crystalline orientationfunction of at least about 0.95, a tensile modulus of at least about 750grams/denier, a tenacity of at least about 20 grams/denier, and a mainmelting temperature of at least about 141° C. (measured at 10° C./minuteheating rate by differential scanning calorimetry), said main meltingtemperature being greater than the main melting temperature of a shapedpolyethylene article of substantially the same weight average molecularweight produced from a polymer solution of substantially the samepolymer concentration, spun at substantially the same throughput rateand subjected to solution stretching at a ratio of less than about 3:1.

The present invention is also drawn to a shaped polyethylene articlehaving a weight average molecular weight between about 200,000 and about4,000,000 a tensile modulus of at least about 350 grams/denier, atransverse microfibrillar spacing which is less than a transversemicrofibrillar spacing of a shaped polyethylene article of substantiallythe same weight average molecular weight produced from a polymersolution of substantially the same polymer concentration, spun atsubstantially the same throughput rate and subjected to solutionstretching at a ratio of less than about 3:1, a tenacity of at leastabout 13 grams/denier, and a main melting temperature of at least about140° C. measured at 10° C./minute heating rate by differential scanningcalorimetry).

The present invention is also directed to novel shaped polyethylenearticles having a weight average molecular weight greater than about200,000 and less than 500,000 a crystalline orientation function of atleast about 0.95, a tensile modulus of at least about 350 grams/denier,a tenacity of at least about 13 grams/denier, and a main meltingtemperature of at least about 140° C. (measured at 10° C./minute heatingrate by differential scanning calorimetry).

The present invention also includes a process for producing shapedpolyethylene articles, for example fibers, which comprises the steps of:

(a) forming, at a first temperature, a solution of polyethylene in afirst solvent, said polyethylene having a weight average molecularweight between about 200,000 and 4,000,000 kilograms/kg mole;

(b) extruding said solution through an aperature to form a solutionproduct, said solution product being at a temperature no less than saidfirst temperature;

(c) stretching the solution product at a stretch ratio of at least about3:1;

(d) cooling the solution product to a second temperature below the firsttemperature to form a first gel containing first solvent;

(e) extracting the first solvent from the first gel with a secondsolvent to form a second gel containing second solvent, substantiallyfree of the first solvent;

(f) drying the gel containing the second solvent to form a xerogelsubstantially free of solvent; and,

(g) stretching at least one of the first gel, the second gel and thexerogel,

the total stretch ratio being sufficient to achieve a polyethylenearticle having a tenacity of at least about 13 grams/denier, a porosityof less than 10% by volume, and a modulus of at least about 350grams/denier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates in schematic form the preferred embodiment of theapparatus used to produce the novel articles.

FIG. 2 graphically depicts the effects of polymer concentration and diedraw ratio on fiber tenacity.

FIG. 3 graphically shows the effects of polymer concentration and diedraw ratio on the overall stretchability of fibers.

DETAILED DESCRIPTION OF THE INVENTION

There are many applications which require load bearing elements of highstrength, modulus, toughness, dimensional and hydrolytic stability.

For example, marine ropes and cables, such as the mooring lines used tosecure tankers to loading stations and the cables used to securedrilling platforms to underwater anchorage, are presently constructed ofmaterials such as nylon, polyester, aramids and steel which are subjectto hydrolytic or corrosive attack by sea water. Consequently, suchmooring lines and cables are constructed with significant safety factorsand are replaced frequently. The greatly increased weight and the needfor frequent replacement creates substantial operational and economicburdens.

The fibers and films of this invention exhibit relatively high strength,high modulus and very good toughness. Also, they are dimensionally andhydrolytically stable. The fibers and films prepared by our uniqueprocess possess these properties in a heretofore unattained combinationand are, therefore, quite novel and useful materials. Consequently, ourfibers and films offer significant advantages when employed as, forexample, marine ropes and cables.

Other applications for the fibers and films of our invention include:reinforcement of thermoplastics, thermosetting resins, elastomers, andconcretes for uses such as pressure vessels, hoses, power transmissionbelts, sports and automotive equipment; and, building constructionmaterials.

The polymer used in the present invention is crystallizablepolyethylene. By the term "crystallizable" is meant a polymer which iscapable of exhibiting a relatively high degree of order when shaped,attributable in part to its molecular weight and high degree oflinearity. As used herein, the term polyethylene shall mean apredominantly linear polyethylene material that may contain minoramounts of chain branching or comonomers not exceeding 5 modifying unitsper 100 main chain carbon atoms, and that may also contain admixedtherewith not more than about 25 wt % of one or more polymeric additivessuch as alkene-1-polymers, in particular low density polyethylene,polypropylene or polybutylene, copolymers containing mono-olefins asprimary monomers, oxidixed polyolefins, graft polyolefin copolymers andpolyoxymethylenes, or low molecular weight additives such asanti-oxidants, lubricants, ultra-violet screening agents, colorants andthe like which are commonly incorporated therewith. In the case ofpolyethylene, suitable polymers have molecular weights (by intrinsicviscosity) in the range of about 200,000 to about 4,000,000. Thiscorresponds to a weight average chain length of 8,333 to 166,666 monomerunits or 16,666 to 333,332 carbons. The preferred weight averagemolecular weight of polyethylene used in our process is between about200,000 (3.2 IV) and about 800,000 (8.4 IV), more preferably betweenabout 250,000 (3-7 IV) and 750,000 (8.0 IV), and most preferably betweenabout 300,000 (4.2 IV) about 700,000 (7.6 IV). The IV numbers representintrinsic viscosity of the polymer in decalin at 135° C. In addition thepolymers used in the present invention have a weight to number averagemolecular weight ratio (Mw/Mn) which is variable over a wide range. Weprefer to use polymers with a Mw/Mn ratio of at least about 5:1 becausepolymers having a more narrow distribution range are more difficult toproduce. In addition, we believe there may be unexpected advantages tousing a higher ratio (i.e. ≧5:1), particularly with a bimodal molecularweight distribution.

The first solvent should be a non-volatile solvent under the processingconditions. This is necessary in order to maintain essentially constantconcentration of solvent upstream and through the aperture (die orspinnerette) and to prevent non-uniformity in liquid content of the gelfiber or film containing first solvent. Preferably, the vapor pressureof the first solvent should be no more than about one fifth of anatmosphere (20 kPa) at 175° C., or at the first temperature. Preferredfirst solvents for hydrocarbon polymers are aliphatic and aromatichydrocarbons of the desired non-volatility and solubility for thepolymer. Preferred first solvents for polyethylene include paraffin ormineral oil.

The polymer may be present in the first solvent in a first concentrationwhich is selected from a range from about 5 to about 25 weight percent.The optimum concentration is dependent upon the polymer molecularweight. For a polymer of about 650,000 (Mw), the first concentration ispreferably about 5 to about 15 weight percent and more preferably about6 to about 10 weight percent; however, once chosen, the concentrationshould not vary adjacent the die or otherwise prior to cooling to thesecond temperature. The concentration should also remain reasonablyconstant over time (i.e., over the length of the fiber or film).

The first temperature is chosen to achieve complete dissolution of thepolymer in the first solvent. The first temperature is the minimumtemperature at any point between where the solution is formed and thedie face, and must be greater than the gelation temperature for thepolymer in the solvent at the first concentration. For polyethylene inparaffin oil at 5 to 15 weight percent concentration, the gelationtemperature is approximately 100°-130° C.; therefore, a preferredtemperature can be between 180° C. and 250° C., or more preferablybetween 200° and 240° C. While temperatures may vary above the firsttemperature at various points upstream of the die face, excessivetemperatures causative of polymer degradation should be avoided. Toassure complete solubility, a first temperature is chosen whereas thesolubility of the polymer exceeds the first concentration, and istypically at least 100 percent greater. The second temperature is chosenwhereas the solubility of the polymer is much less than the firstconcentration. Preferably, the solubility of the polymer in the firstsolvent at the second temperature is no more than about 1% percent ofthe first concentration. Cooling of the extruded polymer solution fromthe first temperature to the second temperature should be accomplishedat a rate sufficiently rapid to form a gel fiber which has substantiallythe same polymer concentration as existed in the polymer solution.Preferably, the rate at which the extruded polymer solution is cooledfrom the first temperature to the second temperature should be at leastabout 50° C./minute.

A critical aspect of our invention is the step of stretching (solutionstretching) the extrudate (solution product) at a ratio of at leastabout 3:1 and up to about 200:1. The preferred ratio of stretchingdepends upon the polymer molecular weight and the first concentration.For a polymer of about 650,000 (Mw) at a first concentration betweenabout 6% and about 10%, the preferred stretch ratio is between about 3:1and about 50:1 and the most preferred ratio of stretching is betweenabout 10:1 and about 50:1. Solution stretching, i.e., stretching thespun solution product prior to forming a gel therefrom, occurs betweenthe aperture of the die and the quench bath (normally within the spaceof a few inches). Stretching can be accomplished by regulating thespinning rate (measured by the length of product formed per unit time)through the die relative to the angular velocity of the quench bathroller. Solution stretching of at least about 3:1 results in theformation of a gel (upon cooling to the second temperature) whichconsist of continuous polymeric networks highly swollen with solvent.Each gel has substantially uniform polymer density with polymer voidsconstituting less than 10% (by volume), normally less than 5%, of thefiber. A solution stretch ratio of at least about 3:1 unexpectedly aidsin forming high strength articles of intermediate molecular weight (cf.U.S. Pat. No. 4,413,110). Within the limitations of the solution stretchratio range, the higher the pump rate of polymer through the die orspinnerette, the lower the solution stretch ratio because of the degreeof alignment (orientation) imparted by shear through the die orspinnerette.

The extraction with second solvent is conducted in a manner (ordinarilyin a washer cabinet) that replaces the first solvent in the gel withsecond solvent without significant changes in gel structure. Someswelling or shrinkage of the gel may occur, but preferably nosubstantial dissolution, coagulation or precipitation of the polymeroccurs. When the first solvent is a hydrocarbon, suitable secondsolvents include hydrocarbons, chlorinated hydrocarbons,chlorofluorinated hydrocarbons and others, such as pentane, hexane,heptane, toluene, methylene chloride, carbontetrachloride,trichlorotrifluoroethane (TCTFE), diethyl ether and dioxane. The mostpreferred second solvents are methylene chloride (B.P. 39.8° C.) andTCTFE (B.P. 47.5° C.). Preferred second solvents are the non-flammablevolatile solvents having an atmospheric boiling point below about 80°C., more preferably below about 70° C. and most preferably below about50° C. Conditions of extractions should be chosen so as to remove thefirst solvent to a level of less than 0.1 percent of the total solventin the gel.

A preferred combination of the conditions is a first temperature betweenabout 150° C. and about 250° C., a second temperature between aboutminus 40° C. and about 40° C. and a cooling rate between the firsttemperature and the second temperature at least about 50° C./minute.Most preferably, the first solvent does not experience a phase change atthe second temperature. It is preferred that the first solvent be ahydrocarbon, when the polymer is a polyolefin such as intermediatemolecular weight polyethylene. The first solvent should be substantiallynon-volatile, one measure of which is that its vapor pressure at thefirst temperature should be less than 20 kPa, and more preferably lessthan 2 kPa.

In choosing the first and second solvents, the primary desireddifference relates to volatility as discussed above. It is alsopreferred that the polymers be less soluble in the second solvent atabout 40° C. than in the first solvent at about 150° C. Once the gelcontaining second solvent is formed, the second gel is then dried underconditions where the second solvent is removed leaving the solid networkof polymer substantially intact. By analogy to silica gels, theresulting material is called a "xerogel" meaning a solid matrixcorresponding to a solid matrix of a wet gel, With the liquid havingbeen replaced by gas (e.g., by in inert gas such as nitrogen or by air).The term "xerogel" is not intended to delineate any particular type ofsurface area, degree of porosity or pore size.

Stretching may be performed upon the gel after cooling to the secondtemperature, or during or after extraction. Alternatively, stretching ofthe xerogel may be conducted, or a combination of gel stretching andxerogel stretching may be preformed. Stretching after gelation mostpreferably is conducted in two or more stages. The first stage ofstretching may be conducted at room temperature or at an elevatedtemperature, ordinarily at a temperature between about 115° C. and 135°C. Preferably, stretching is conducted in the last of the stages at atemperature between about 120° C. and 155° C. Most preferably, thestretching is conducted in the last of the stages at a temperaturebetween about 135° C. and 150° C.

The stretching which occurs subsequent to gelation is another criticalaspect of our invention. Stretching subsequent to gelation can beaccomplished during quenching, washing, and/or drying of the gels, andcan also be accomplished by a xerogel stretching step. As noted above,stretching subsequent to gelation most preferably occurs in at least twostages. The amount of acceptable stretching subsequent to gelation atvarious stages of the process is as follows: stretching of the gels isnormally at least about 1.5:1; stretching of the xerogel in a firststage, preferably occurring between 115° C. and 135° C., is generallymore than about 2:1; and stretching of the xerogel in a second stage,preferably occurring between about 130° C. and 155° C., is normallyabout 1.5:1.

With a solution stretch ratio of at least about 3:1 and at least onesubsequent stretching operation, the overall stretch ratio of theproduct is between about 30:1 and about 500:1 or more. The totalcombined stretch ratio (of the solution product, the gel and/or thexerogel) of at least about 30:1 produces novel articles exhibiting aunique combination of properties. Furthermore, the stretching steps ofthe process are interrelated in such a fashion that an increase in thesolution stretch ratio is coupled with a decrease in the subsequent geland/or xerogel stretch ratios. The Examples described hereinbelowillustrate how the stretch ratios are interrelated in obtainingparticular improved fiber properties.

The intermediate weight polyethylene articles, such as fibers, producedby the present process are novel in that they exhibit a uniquecombination of properties: a tensile modulus at least about 350grams/denier (preferably at least about 500 grams/denier, morepreferably at least about 750 grams/denier, and most preferably at leastabout 1,000 grams/denier), a tenacity at least about 13 grams/denier(preferably at least about 15 grams/denier, more preferably at leastabout 18 grams/denier and most preferably at least about 20grams/denier), a main melting temperature (measured at 10° C./minuteheating rate by differential scanning calorimetry) of at least about140° C., preferably at least about 141° C., and wherein said mainmelting temperature is greater than the main melting temperature of ashaped polyethylene article of substantially the same weight averagemolecular weight produced from a polymer solution of substantially thesame polymer concentration, spun at substantially the same throughputrate and subjected to solution stretching at a ratio of less than about3:1, a porosity of less than 10% by volume (normally less than 5%), anda crystalline orientation function (f.sub.ε) of at least about 0.95.Preferably, the article has an ultimate elongation (UE) at most of about7 percent, and more preferably not more than about 5 percent. Inaddition, the articles have a high toughness and uniformity. Moreoverand very importantly, the products produced by our process exhibit atransverse microfibrillar spacing less than that which would occur in anarticle of the same molecular weight having been produced by a processwhich subjects a solution product to a solution stretch of less thanabout 3:1.

The crystalline orientation function is a measurement of the degree ofalignment of the axis of the polymer crystals with the major axis of theproduct. It has been shown that the higher the crystalline orientationfunction the higher the tensile strength of the product. The crystallineorientation function is mathematically calculated from the equationreported by R. S. Stein, J. Poly. Sci., 31, 327 (1958): ##EQU1## whereθ=the angle between the major axis of the product and the major axis ofthe crystals in the product. Perfectly oriented crystals, i.e. crystalhaving a major axis parallel to the major axis of the product, wouldexhibit an f.sub.ε =1. For polyethylene fibers produced by our novelprocess, the crystalline orientation function is at least about 0.95.

We have also employed infra-red techniques to determine the overallorientation function for a polyethylene product produced by our process.This technique is reported in detail in R. J. Samuels, Structure ofPolymers and Properties, John Wiley and Sons, New York, 1974, pp. 63-82.

The degree of crystallinity of the product is related to the tensilestrength in a similar fashion as the orientation factor. Crystallinityof the product can be measured by a variety of methods including x-raydiffraction, heat of fusion and density measurement and is at leastabout 0.70 or higher. By x-ray diffraction, we measured the degree ofcrystallinity of a fibrous product produced by our process to be about0.65. However, density measurements of the same fiber indicate a degreeof crystallinity of about 0.77. See Example 13.

An important and unique property of products produced by our process isthe transverse microfibrillar spacing. Products produced by our processexhibit microstructure (transverse microfibrillar spacing) below about150 Å that appears to be sensitive to the critical process variables andmay have a direct role in the final properties of the product. Thespacing between the microfibrils i.e., the transverse microfibrillarspacing, is unique in that an article produced by employing a solutionstretch of at least about 3:1 exhibits a transverse microfibrillarspacing less than that which would exist in a shaped polyethylenearticle of substantially the same weight average molecular weightproduced from a polymer solution of substantially the same polymerconcentration, spun at substantially the same throughput rate andsubjected to solution stretching at a ratio of less than about 3:1. Fromsome preliminary small angle x-ray scattering investigations conductedwith fiber products, we believe that products produced by our processwill have a transverse microfibrillar spacing of less than about 50 Å.Our small angle scattering investigations were carried out using Curadiation (1.54 Å, Ni filtered). In the procedure, the x-rays, directednormal to the major axis of the fiber, impact the fiber and arescattered over an angle 2θ≦5°. The intensity (I) of the scattered x-raysare detected over the entire angle 2θ using a linear position sensitiveproportional counter. The intensity (I) is plotted versus the angle toestablish a peak intensity (indicated at a specific angle) which ischaracteristic of the transverse microfibrillar spacing (the spacingbeing calculated from Braggs Law λ=2d sin θ, which is assumed to becorrect).

As indicated in the Examples below, tradeoffs between various propertiescan be made in a controlled fashion with the present process.

FIG. 1 illustrates in schematic form the preferred embodiment of theapparatus used to produce novel fibers, wherein the stretching stepsinclude solution filament stretching and stretching at least two of thegel containing the first solvent, the gel containing second solvent;and, the xerogel. As shown, a first mixing vessel 10 is fed with theintermediate molecular weight polymer 11 such as polyethylene of weightaverage molecular weight between about 200,000 and about 4,000,000, andis also fed with a first, relatively non-volatile solvent 12 such asparaffin oil. First mixing vessel 10 is equipped with an agitator 15.The residence time of polymer and first solvent in first mixing vessel10 is sufficient to form a slurry. The slurry is removed from firstmixing vessel via line 14 to a preheater 15. The residence time andtemperature in preheater 15 are sufficient to dissolve between about 5%and 50% of the polymer. From the preheater 15, the solution is fed to anextrusion device 18 containing a barrel 19 within which is a screw 20operated by motor 22 to deliver polymer solution at reasonably highpressure to a gear pump in housing 23 at a controlled flow rate. Motor24 is provided to drive gear pump 23 and extrude the polymer solution,still hot, through a spinnerette at 25 comprising a plurality ofaperatures, which may be circular, x-shaped or oval shaped, or in any ofa variety of shapes having a relatively small major access in the planeof the spinnerette when it is desired to form fibers, and having aregtangular or other shape when an extended major access in the plane ofthe spinnerette when it is desired to form films or tapes.

An aperture of circular cross section (or other cross section without amajor axis in the plane perpendicular to the flow direction more thanabout 8 times the smallest axis in the same plane, such as oval, y- orx-shaped aperture) is used so that both gels will be fiber gels, thexerogel will be a xerogel fiber and the product will be a fiber. Thediameter of the aperture is not critical, with representative aperturesbeing between about 0.25 mm and about 5 mm in diameter (or other majoraxis). The length of the aperture in the flow direction should normallybe at least about 10 times the diameter of the aperture (or othersimilar major access), preferably at least 15 times and more preferablyat least 20 times the diameter (or other similar major access).

The temperature of the solution in the preheater vessel 15, in theextrusion device 18 and at the spinnerette 25 should all equal or exceeda first temperature (e.g., about 200° C.) chosen to exceed the gelationtemperature (approximately 100° to 130° C. for polyethylene and paraffinoil). The temperature may vary (fluctuating between about 200° C. and220° C.) or maybe constant (e.g., about 220° C.) from the preheatervessel 15 to the extrusion device 18 to the spinnerette 25. At allpoints, however, the concentration of polymer in the solution should besubstantially the same. The number of aperatures in thus the numbers offibers formed, is not critical, with convenient number of fibers being16, 19, 120 or 240.

From the spinnerette 25, the polymer solution passes through an airgap27, optionally enclosed and filled with an inert gas such as nitrogen,and optionally provided with a flow of gas to facilitate cooling. Aplurality of solution fibers 28 containing first solvent pass throughthe airgap 27 and into a quench bath 30 so as to cool the fibers, bothin the airgap and in the quench bath 30 to a second temperature at whichthe solubility of the polymer in the first solvent is relatively low,such that the polymer solution forms a gel. Prior to gelation, solutionfiber stretching occurs in the airgap 27 at a ratio of at least about3:1. This high stress draw of the solution fibers prior to gelation iscritical in achieving the ultimate properties of the fibers.

Rollers 31 and 32 in the quench bath operate to feed the fiber throughthe quench bath and operate in relation to the solution fiber rate ofextrusion (determined by the length of extruded fiber per unit time) atan angular velocity sufficient to stretch the solution filament at aratio of at least about 3:1 prior to gelation. As between rollers 31 and32, it is contemplated that stretching of the gel filament may bedesired. Normally, the degree of stretch imparted between roll 31 and 32to the gel fiber would be more than about 1.5:1. In the event thatstretching of the gel fiber between rollers 31 and 32 is desired, someof first solvent may exude out of the fibers and can be collected as alayer in quench bath 30. From the quench bath 30, the cool first solventcontaining gel fibers (first gel fibers) 33 passed to a solventextraction device 37 where a second solvent, being of relatively lowboiling point, such as trichlorotrifluoroethane, is fed in through line38. The solvent outflow through line 40 contains second solvent andsubstantially all of the first solvent from the cool first gel fibers33. The polymer is now swollen by the second solvent. Thus, secondsolvent containing gel fibers (second gel fibers) 41 conducted out ofthe solvent extraction device 37 contain substantially only secondsolvent, and relatively little first solvent. The second gel fibers 41may have shrunken somewhat compared to the first gel fibers 33, butotherwise have substantially the same polymer morphology.

In a drying device 45, the second solvent is evaporated from the secondgel fibers 41 forming essentially unstretched xerogel fibers 47 whichare taken up on spool 52.

From spool 52, or from a plurality of spools if it is desired to operatea stretching line at a slower feed rate than the take up line of spool52 permits, the fibers are fed over driven feed roll 54 and idler roll55 into a first heated tube 56 which may be rectangular, cylindrical orany other convenient shape. Sufficient heat is supplied to the tube 56to cause the internal temperature to be between about 115° C. and 135°C. The fibers may be stretched at this stage if desired. In thisembodiment stretching would occur at a relatively high ratio (generallymore than about 2:1, preferably about 3:1) so as to form partiallystretched fibers 58 taken out by a driven roll 61 and idler roller 62.From rolls 61 and 62, the fibers are taken through a second heated tube63, heated so as to be at somewhat higher temperature, e.g., 130° C. toabout 155° C., and are then taken up by driven takeup roll 65 and idlerroll 66. The driven takeup roll 65 is capable of operating at asufficient speed to impart a desired stretch ratio to the gel fibers inheated tube 63 (normally more than about 1.1:1, preferably between about1.2:1 and about 1.7:1). The twice stretched fiber 68 produced in thisembodiment are taken up on takeup spool 72.

With reference to FIG. 1, the seven process steps of the invention canbe seen. The solution forming step (a) is conducted in preheater 15 andextrusion device 18. The extrusion step (b) is conducted with device 18and 23, and especially through spinnerette 25. The solution productstretching step (c) is generally conducted in the airgap 27, and thecooling and quenching step (d) is conducted in the airgap 27 and in thequench bath 30. Extraction step (e) is conducted in solvent extractiondevice 37. The drying step (f) is conducted in the drying device 45. Thestretching step (g) is preferably conducted in elements 52-72, andespecially in heated tubes 56 (Zone 1) and 63 (Zone 2). It will beappreciated however, that various other parts of the system may alsoperform some stretching, even at temperatures substantially below thoseof heated tubes 56 and 63. As noted before, stretching may occur withinthe quench bath 30, within the solvent extraction device 37, withindrying device 45 and/or between solvent extraction device 37 and dryingdevice 45.

EXAMPLE 1 Xerogel Yarn Preparation

A HELICONE oil jacketed double Helical mixer, constructed by AtlanticResearch Corporation, was charged with 10 wt % linear polyethylene, 89.5wt % mineral oil (Witco "Kaydol"), and 0.5 wt % antioxidant (Shell"Ionol").

The linear polyethylene was Allied Corporation FD60-018 having anintrinsic viscosity (IV) of 3.7 measured in decalin at 135° C., a weightaverage molecular weight of 284,000 kg/mol and an Mw/Mn of approximately10. The charge was heated with agitation at 60 rpm to 240° C. The bottomdischarge opening of the Helicone mixer was adapted to feed the polymersolution first to a gear pump and then to a 19-hole spinning die. Theholes of the spinning die were each of 0.040" diameter. The gear pumpspeed was set to deliver 15.2 cm³ /min of polymer solution to the die.The extruded solution filaments were stretched 39.8:1 in passing througha 2" air gap into a water quench bath at 15° C. wherein the filamentswere quenched to a gel state.

The gel "yarn" was passed into a washer cabinet in which the mineral oilcontent of the gel filaments was extracted and replaced bytrichlorotrifluoroethane (TCTFE) at 35° C. The gel yarn was stretched1.14:1 in traversing the washer. The extracted gel yarn was passed intoa dryer cabinet where the TCTFE was evaporated free the yarn at 60° C.The dried yarn was stretched 1.14:1 at 60° C. as it exited the dryercabinet. The extracted and dried xerogel yarn of 173 denier was woundonto a roll at 63.2 meters/min.

EXAMPLES 2-9 Hot Stretching

The roll of xerogel yarn from Example 1 was transferred to a two-zonestretch bench. Each zone consisted of a 10-ft long heated tubemaintained at uniform temperature and under nitrogen blanketing. Thexerogel yarn was fed into the first stage at 16 m/min. Other stretchconditions and the properties of the yarns obtained are given in Table2.

                  TABLE 2                                                         ______________________________________                                               ZONE TEMPS, °C.                                                                      STRETCH RATIOS                                           Example  #1       #2         #1     #2                                        ______________________________________                                        2        120      136        3.0    1.5                                       3        120      135        3.0    1.5                                       4        120      145        2.9    1.6                                       5        120      145        2.9    1.7                                       6        125      140        3.0    1.5                                       7        129      145         2.75   1.35                                     8        129      145         2.75   1.45                                     9        130      145        3.0    1.5                                       ______________________________________                                                                  Modulus        W-t-B*                               Example                                                                              Denier    Tenacity g/d      % UE  J/g                                  ______________________________________                                        2      47        14       490      5.5   43                                   3      52        13       460      6.0   46                                   4      40        13       470      7.2   59                                   5      45        12       430      8.2   64                                   6      34        14       550      5.6   46                                   7      40        12       380      9.2   77                                   8      38        12       410      8.2   66                                   9      31        15       490      8.7   83                                   ______________________________________                                         *W-t-b is the work needed to break the fiber.                            

The melting temperatures of the yarns of examples 6 and 9 weredetermined using a Perkin-Elmer DSC-2 Differential Scanning Calorimeter.Samples of about 3.2 mg were heated in argon at the rate of 10° C./min.The yarns showed a doublet endotherm in duplicate runs:

    ______________________________________                                        Example 6      142° C.                                                                        (main) + 146° C.                                Example 9      140° C.                                                                        (main) + 148° C.                                ______________________________________                                    

EXAMPLES 10-31 Xerogel Yarn Preparation and Hot Stretching

The xerogel yarns of the following examples were prepared from solutionsof polyethylene (Mitsui HI-ZEX 145M-60) having a 7.1 IV (a weightaverage molecular weight of 649,000 kg/mole) and an Mw/Mn ofapproximately 8. The xerogel yarns were prepared essentially as inExample 1 except that the spinning solution concentrations, the pumpingrate, the stretch of the solution yarns and the stretch of the gel yarnswere varied as illustrated in Table 3. The gel yarn stretch ratiosemployed in Examples 10-31 were generally the highest that could beemployed consistent with either of two constraints: breakage of theyarn, or physical limitations of the apparatus used. In general,physical limitations of the apparatus limited the gel yarn stretch ratiothat could be employed with yarns spun with a solution stretch of aboveabout 20:1. Therefore, the gel yarn stretch ratios recited in theExamples should not be construed as fundamental limitations of theprocess as higher gel stretch ratios can be employed.

                  TABLE 3                                                         ______________________________________                                                Solution  Pumping    Stretch Ratios                                           Conc.,    Rate       Solution                                                                              Gel                                      Example Wt %      cm.sup.3 /min                                                                            Yarn    Yarn                                     ______________________________________                                        10      6         38         1.1     9.02                                     11      6         38         3.1     4.5                                      12      6         15.2       8.8     3.39                                     13      6         15.2       8.8     3.39                                     14      6         15.2       29.0    1.85                                     15      6         15.2       46.6    1.15                                     16      8         38         1.1     9.62                                     17      8         15.2       3.16    5.61                                     18      8         15.2       8.65    3.4                                      19      8         15.2       36.8    1.46                                     20      10        38         1.09    8.44                                     21      10        29.2       3.25    7.34                                     22      10        12.8       8.74    7.43                                     23      10        16.4       19.4    2.78                                     24      12        38         1.1     8.94                                     25      12        15.2       18.1    2.97                                     26      12        15.2       26.7    2.02                                     27      12        15.2       38.2    1.41                                     28      15        15.6       1.1     8.6                                      29      15        15.6       18.2    3.0                                      30      15        15.2       26.7    2.0                                      31      15        15.6       38.6    1.39                                     ______________________________________                                        Stretch Ratios                                                                        Leaving   Zone No. 1 Zone No. 2                                       Example Dryer     @ 120° C.                                                                         @ 145° C.                                                                       Overall                                 ______________________________________                                        10      1.24      3.0        1.35     50                                      11      1.3       3.75       1.4      95                                      12      1.22      2.9        1.4      147                                     13      1.22      2.9        1.5      158                                     14      1.14      3.6        1.4      308                                     15      1.14      3.5        1.4      299                                     16      1.25      3.3        1.2      52                                      17      1.26      4.5        1.3      131                                     18      1.20      4.9        1.3      184                                     19      1.14      5.5        1.4      472                                     20      1.24      2.75       1.4      44                                      21      1.17      3.0        1.5      126                                     22      1.14      2.75       1.4      285                                     23      1.14      3.9        1.5      360                                     24      1.31      2.75       1.4      50                                      25      1.14      3.9        1.5      276                                     26      1.14      2.8        1.4      241                                     27      1.14      3.5        1.4      301                                     28      1.19      2.5        1.2      34                                      29      1.14      2.25       1.4      196                                     30      1.14      2.25       1.5      205                                     31      1.14      3.0        1.3      239                                     ______________________________________                                    

The xerogel yarns were hot stretched as in Examples 2-9. Zone No. 1temperature was maintained at 120° C. and Zone No. 2 temperatures was145° C. The stretch ratios and the properties of the yarns obtained aregiven in Table 4.

                                      TABLE 4                                     __________________________________________________________________________              Tenacity                                                                           Modulus                                                                            %   W-t-B.sup.1                                           Example                                                                            Denier                                                                             g/d  g/d  UE  J/g  Melting Temps °C.*                        __________________________________________________________________________    10   119  24   1100 3.5 47   --                                               11   65   26   1380 3.7 54   --                                               12   41   30   1340 3.7 63   146, 151                                         13   46   29   1030 4.4 73   --                                               14   20   29   1480 3.3 58   146, 151                                         15   19   24   1040 4.1 56   134, 146, 148                                    16   187  24   1100 3.5 46   146, 151                                         17   90   19   790  4.4 49   --                                               18   50   30   1380 4.0 69   --                                               19   16   30   1180 4.5 74   146, 151                                         20   289  24   1040 3.9 50   --                                               21   84   31   1280 4.6 80   146, 151                                         22   45   28   1030 4.4 66   --                                               23   33   28   860  4.8 74   --                                               24   291  24   1290 3.5 47   --                                               25   43   28   1050 5.2 81   142, 150                                         26   44   28   870  6.1 90   --                                               27   44   27   840  6.5 96   144, 149                                         28   510  21   880  4.3 47   --                                               29   92   20   640  5.8 61   --                                               30   84   20   680  6.3 64   --                                               31   45   22   650  5.4 60   --                                               __________________________________________________________________________     *Main melting peak is underlined                                              .sup.1 Wt-b is the work needed to break the fiber.                       

It is seen from the data of Examples 10-31 that yarn tenacity, modulus,elongation, toughness and melting temperatures may be regulated througha choice of solution concentration, solution stretch ratio, gel stretchratio and xerogel stretch ratios. The yarn properties are also functionsof polymer IV and the respective stretch temperatures and speeds. Thefinal product of Example 13 was characterized by x-ray diffraction, heatof fusion, density, and infra-red dichroic measurements at 720 and 730cm⁻¹. The results are as follows:

a) density (Kg/m³): 961

b) heat of fusion (cal/g): 59.6

c) x-ray crystallinity index: 0.65

d) crystalline orientation function (f.sub.ε): 0.992

e) overall infra-red fiber orientation function: 0.84.

The tenacity data of Examples 10-31 are shown plotted vs. solutionstretch ratio in FIG. 2. Examples 10, 16, 20, 24 and 28 are comparativeexamples of fiber samples not subject to a solution stretch of at leastabout 3:1. Surprisingly, it is apparent from the plot that for this 7.1IV polymer essentially the same tenacity-solution stretch ratiorelationship applies for polymer concentrations of from 6 wt % to 10 wt%.

In FIG. 3, the overall stretch ratios obtained in Examples 10-31 areshown plotted vs. solution stretch ratio and as a function of polymerconcentration. Very surprisingly, the stretchability (overall stretchratio) increased with increasing polymer concentration over theconcentration range 6 wt %-10 wt %. This feature is contrary to reportsin the literature which clearly indicate that as concentration levelsincrease, the overall stretchability of the fiber should decrease. SeeSmith, Lemstra & Booij, Journal of Polymer Science, Poly. Phys. Ed., 19,877 (1981). While the causes of the opposite effect indicated by ourresults as compared to the results reported in Smith et al., supra, arenot entirely clear, it appears that this opposite effect results fromthe sequence of processing steps employed in our process (which producesa more uniform fiber).

Our results indicate that solution stretching at a ratio of at least 3:1tends to cause molecular disentanglement. Because this feature competeswith the opposing tendency of greater entanglement with increasingpolymer concentration, we believe that optimum overall stretchabilityoccurs at intermediate solution stretch ratios and intermediate firstconcentrations.

EXAMPLES 32-36

The xerogel yarns of the following examples were prepared from a 6 wt %solution of polyethylene (Hercules HB-301) having a 9.0 IV,approximately 998,000 Mw, and an Mn/Mm of approximately 8. The yarnswere spun essentially as in Example 1 except that the solution yarns andgel yarns were stretched as recited in Table 5. Pumping rate was 38 cm³/min in Examples 32 and 33 and was 17.3 cm³ /min in Examples 34-36. Thexerogel yarns were hot stretched as in Examples 2-9. Zone No. 1temperature was maintained at 135° C. and zone No. 2 temperature was150° C. Feed speed to the first hot stretch zone was 12 m/min in Example32, 24 m/min in Example 33 and 16 m/min in Examples 34-36. The stretchratios and the properties of the yarns obtained are also given in Table5.

                                      TABLE 5                                     __________________________________________________________________________    Stretch Ratios                                                                     Solution                                                                           Gel  Leaving                                                                            Zone No. 1                                                                           Zone No. 2                                         Example                                                                            Yarn Yarn Dryer                                                                              @ 135° C.                                                                     @ 150° C.                                                                     Overall                                     __________________________________________________________________________    32   1.08 8.14 1.3  3.25   1.2    45                                          33   1.08 8.14 1.3  2.5    1.2    34                                          34   12.95                                                                              3.65 1.15 3.0    1.2    196                                         35   19.8 2.38 1.15 3.0    1.25   203                                         36   40.0 1.18 1.15 3.0    1.25   203                                         __________________________________________________________________________                      Tenacity                                                                            Modulus                                                                             %   W-t-B*                                              Example                                                                            Denier                                                                             g/d   g/d   UE  j/g                                         __________________________________________________________________________            32   151  22    1120  2.9 35                                                  33   149  25    1160  3.3 43                                                  34   28   31    1360  3.7 63                                                  35   26   32    1370  3.7 64                                                  36   21   29    1040  4.2 65                                          __________________________________________________________________________     *W-t-b is the work needed to break the fiber.                            

EXAMPLES 37-47

The following examples illustrate that the maximum attainable solutionstretch and the effects of solution stretch are dependent on polymermolecular weight, solution concentration and spinning throughput rate.

In these examples, polyethylene solutions were prepared as in Example 1except that the polymer was of 26 IV, approximately 4.5×10⁶ Mw, andMw/Mn of approximately 8. The solutions were spun through a 16 holespinning die whose holes were of 0.040" diameter. The pumping rate was16 cm³ /min in Examples 37-39 and 41, 32 cm³ /min in Example 40, and 48cm³ /min in Examples 42-47.

                  TABLE 6                                                         ______________________________________                                        Stretch Ratios                                                                        Solution Gel     Zone No. 1                                                                            Zone No. 2                                   Example Yarn     Yarn    @ 135° C.                                                                      @ 150° C.                                                                      Overall                              ______________________________________                                        37      0.61     6.78    5.25    2.0     43                                   38      11.21    5.6     4.75    2.0     64                                   39      3.05     3.1     5.5     2.0     104                                  40      5.56     1.0     4.75    3.0     79                                   41      10.0     1.0     4.5     2.5     112                                  42      11.0     (BROKE)------------------------------------                  43      1.08     3.7     5.75    2.25    52                                   44      1.48     2.58    5.0     2.5     48                                   45      2.25     1.95    5.35    2.5     59                                   46      3.82     1.0     5.0     2.75    52                                   47      4.0      (BROKE)------------------------------------                  ______________________________________                                                                  Modulus       W-t-B*                                Example Denier  Tenacity  g/d     % UE  j/g                                   ______________________________________                                        37      174     31        1620    2.7   92                                    38      92      32        2250    2.4   --                                    39      62      33        2090    2.5   --                                    40      59      31        1690    2.7   --                                    41      38      33        1880    2.7   --                                    42                                                                            43      138     32        1630    2.5   --                                    44      130     35        1710    2.8   --                                    45      99      32        1580    2.6   --                                    46      108     28        1160    3.3   --                                    47                                                                            ______________________________________                                         *W-t-b is the work needed to break the fiber.                            

We claim:
 1. A film or fiber consisting essentially of polyethylenehaving a weight average molecular weight between about 200,000 and lessthan 800,000 kg/kg mole, said fiber or film having a tensile modulus ofat least 350 grams/denier, a tenacity of at least 13 grams/denier, acrystalline orientation function of at least 0.95, a main meltingtemperature of at least 140° C. (measured at 10° C./minute heating rateby differential scanning calorimetry), an ultimate elongation of notmore than 5%, and a traverse microfibrillar spacing of less than 150 Å.2. The fiber or film of claim 1 wherein the polyethylene has a weightaverage molecular weight between 250,000 and 750,000, and the fiber orfilm has a tensile modulus of at least 500 grams/denier and a tenacityof at least 15 grams/denier.
 3. The fiber or film of claim 2 wherein thefiber or film has a tensile modulus of at least 750 grams/denier and atenacity of at least 18 grams/denier.
 4. The fiber or film of claim 1wherein the main melting temperature is at least 141° C.
 5. The fiber orfilm of claim 4 wherein the polyethylene has a weight average molecularweight between 300,000 and 700,000, and the fiber or film has a tensilemodulus of at least 750 grams/denier and a tenacity of at least 20 gramsdenier.
 6. The fiber or film of claim 4 wherein the tensile modulus isat least 1000 grams/denier and the tenacity is at least 20 grams/denier.7. The fiber or film of claim 1 further having a crystallinity of atleast 70%.
 8. The fiber or film of claim 1 wherein the porosity is lessthan 10% by volume.
 9. A film or fiber consisting essentially ofpolyethylene having a weight average molecular weight between 200,000and 800,000 kg/kg mole, said fiber or film having a tensile modulus ofat least 350 grams/denier, a tenacity of at least 13 grams/denier, acrystalline orientation function of at least 0.95, a main meltingtemperature of at least 140° C. (measured at 10° C./minute heating rateby differential scanning calorimetry), an ultimate elongation of notmore than 5%, and said fiber or film having been produced by a solutionspinning process in which a solution of the polyethylene is subjected tostretching at a ratio of at least 3:1.
 10. Yarn comprising polyethylenefiber having a weight average molecular weight between 200,000 and800,000 kg/kg mole, said fiber or film having a tensile modulus of atleast 350 grams/denier, a tenacity of at least 13 grams/-denier, acrystalline orientation function of at least 0.95, a main meltingtemperature of at least 140° C. (measured at 10° C./minute heating rateby differential scanning calorimetry), an ultimate elongation of notmore than 5%, and a traverse microfibrillar spacing of less than 150 Å.11. A film or fiber consisting essentially of polyethylene having aweight average molecular weight between 200,000 and 500,000 kg/kg mole,said fiber or film having a tensile modulus of at least 350grams/denier, a tenacity of at least 13 grams/denier, a crystallineorientation function of at least about 0.95, a main melting temperatureof at least 140° C. (measured at 10° C./minute heating rate bydifferential scanning calorimetry), an ultimate elongation of not morethan 5%, and said fiber or film having been produced by a solutionspinning process in which a solution of the polyethylene is subjected tostretching at a ratio of at least 3:1.
 12. A film or fiber consistingessentially of polyethylene having a weight average molecular weightbetween 200,000 and 4,000,000 kg/kg mole, said fiber or film having atensile modulus of at least 350 grams/denier, a tenacity of at least 13grams/denier, a crystalline orientation function of at least 0.95, amain melting temperature of at least 140° C. (measured at 10° C./minuteheating rate by differential scanning calorimetry), an ultimateelongation of not more than 5%, and a traverse microfibrillar spacing ofless than 150 Å.
 13. A film or fiber consisting essentially ofpolyethylene having a weight average molecular weight between 200,000and less than 4,000,000 kg/kg mole, said fiber or film having a tensilemodulus of at least 350 grams/denier, a tenacity of at least 13grams/denier, a crystalline orientation function of at least 0.95, amain melting temperature of at least 140° C. (measured at 10° C./minuteheating rate by differential scanning calorimetry), an ultimateelongation of not more than 5%, and said fiber or film having beenproduced by a solution spinning process in which a solution of thepolyethylene is subjected to stretching at a ratio of at least 3:1.